Cardiac index

Cardiac index (CI) is a haemodynamic parameter that relates the cardiac output (CO) to body surface area (BSA), thus relating heart performance to the size of the individual. The unit of measurement is litres per minute per square metre (l/min/m²).

Calculation

The index is usually calculated using the following formula:

$CI = \frac{CO}{BSA} = \frac{SV*HR}{BSA}$

where

CI=Cardiac index

BSA=Body surface area

SV=Stroke volume

HR=Heart rate

CO=Cardiac output

Clinical significance

The normal range of cardiac index in rest is 2.6 - 4.2 L/min per square meter.

It is frequently measured and used in intensive care medicine, and cardiac intensive care. It is a useful marker of how well the heart is functioning as a pump by directly correlating the volume of blood pumped by the heart with an individual's body surface area.

If the CI falls below 1.8 L/min/m², the patient may be in cardiogenic shock.